Cavity resonator electron



EXAMIN orig. 2557,78()

2 sims-SMT 1 W. C. BROWN CAVITY RESONATOR ELECTRON DISCHARGE DEVICE April 29,1952

Original Filed April 19, 1947 yApril 29, 1952 w. c. BROWN cAvrTY RESONATOR ELEcTRoN DISCHARGE DEVICE 2 SHEETS-SHEET 2 Original Filed April 19. 1947 /NvENro/ W/LL/AM C. B/ow/v 5" 8% al Argo/:Nev

Reissued Apr. 29, 1952 CAVITY RESONATOR ELECTRON DISCHARGE DEVICE William C. Brown, Weston, Mass., assigner to Raytheon Manufacturing Company, Newton, Mass., a corporation of Dslaware Original No. 2,557,780, dated June 19, 1951, Serial No. 742,541, April 19, 1947. Application for reissue November 20, 1951, Serial No. 257,397

7 Claims. (Cl. 315-39) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to electron discharge devices having a plurality of cavity resonators. and more particularly to those for generating oscillations of short wave length.

One of the objects oi' the present invention is to provide a device of the tyre referred to which shall have an improved symmetrical coupling for all of the cavity resonators, by which the ratio of energy actually delivered, to that generated by the device, is materially increased.

The above object and such other aims and objects of the present invention as may hereinafter appear will be best understood from the following description, taken in connection with the accompanying drawings of several embodiments of the invention herein presented for illustrative purposes.

In the drawings:

Fig. 1 is a central, longitudinal section of an electron discharge device. as viewed along line I-I of Fig. 3, incorporating one illustrative ernbodiment of the invention:

Fig. 2 is a partial, longitudinal section oi an electron discharge device incorporating a second illustrative embodiment of the present invention;

Fig. 3 is a horizontal cross-sectional on line 3-3 of Fig. 1;

Fig. 4 is a. perspective view showing the energy transferring means of the output coupling and how it cooperates with the resonant cavities;

Fig. 5 is a partial longitudinal section of an electron discharge device incorporating a third illustrative embodiment of the present invention:

Figs. 6 and T are schematic diagrams of equivalent circuits oi the electron discharge device;

Fig. 8 is a sketch of the embodiment shown in Fig. 5 for the purpose of mathematical calculations utilized to determine the electrical connections of the electron discharge device;

Fig. 9 is an equivalent circuit of the sketch shown in Fig. 8; and

Fig. 10 is a view along the axis of the electron discharge device illustrated in Fig. 8 showing the relative disposition of the prongs of the energytransferring means for purposes of mathematical calculations.

'I'he invention is herein illustratively shown and described in its application to that type of electron discharge device known as a magnetron.

Referring now to Fig. l, there is shown a cylin drical member I U having soldered to its inner surface a plurality of suitably spaced, radially disposed anode arms II, the inner edge surfaces of which constitute anode faces I2. drical member and anode arms are preferably made of copper and said anode surfaces are dis- Said cylinposed substantially parallel to an electron-emissive cathode I3. For example, said cathode may be a slotted tungsten cylinder suitably supported axially of said anode surfaces. Each pair o1' said anode arms Il, with the intervening portion of said cylindrical member I0, constitutes a cavity resonator I4, see Fig. 3.

The cylindrical member IU is hermetically sealed at both ends. thus forming a hermetically sealed envelope or enclosure. In the illustrative embodiment of Fig. l, a disc member I5 and vitreous member I6 are used to complete the aforementioned envelope. The member I5, preferably constructed of copper, is suitably apertured, as at IB, to receive, as by soldering. a tubular member I1, or the disc I5 and tubular member I'I may be constructed as a unitary member.

Concentrically disposed within said cylindrical member are a pair of pole pieces Ill-20. Said pole pieces are partially cylindrical and partially the frustum of a cone. The smaller of the two parallel areas of said frustum serves to concentrate any magnetic eld present between said pole pieces. The pole piece I9 is disposed within that portion of the envelore providing ingress for a cathode lead-in and supporting member 2|. Both of the pole pieces are provided, respectively, with hores 22-23, the bore 92 being in register with the aperture I8. The other pole piece 20 is disposed within an electrically conductive member in the form of a cylindrical cap 24. Said cap is Preferably made of copper, the oren end being disposed in slots IIA provided in alternate anode arms II. Integral with the at portion 25 of said cap is the open end of an electrically conductive tubular member 2S, preierablv made of copper. The opposite open end of said tubular member is hermetically sealed along its edge in an arerture 21 in the vitreous rner^ber I6. the particular arrangement just described being adapted to receive an inner conductor 28 of a coaxial transmission line comprising said inner conductor 28 and an outer conductor 29. Intermediate said outer conductor 29 and the envelope I0 is a tubular member 30. This tubular member is adjusted so that, between points A and B, the distance is equal to a half wavelength of the operating frequency of the electron discharge deviceA When so adjusted it serves in the capacity of a radio frequency choke in a manner well known to those skilled in the art to which it pertains.

if the above-described device be'energized and a lCnfrit-dinal eld be excited within the device by suitable means, as for example by supplying said pole pieces I9-2l with a magnetic field from an external magnet, oscillations will be generated in the cavity resonators I4 which may be led out of the device to a suitable utilizing circuit by means of the novel coupling device just described, comprising the cap 24 and tubular member 26.

In operation, the polarity of the anode arms II is constantly shifting, alternate arms being always of the opposite polarity to that of the intervening arms. By its connection with the alternate arms, the coupling cap 24 transfers the energy of said alternate arms to the tubular member 26 and thence to the inner conductor 28. while that from the intervening anode arms is transferred through the envelope IU, the tubular member 30 to the outer conductor 29. Since said conductors 28 and 29 form the inner and outer conductors, respectively, of a coaxial line, the energy collected by said coupling cap 24 is caused to ow out due to the difference of potential of said two conductors.

Fig. 2 is an alternative embodiment adapted for connection to a. wave guide system. In this particular embodiment, the cap 24 is surmounted by a dome-shaped cap 3| which may serve as an exciting probe for a wave guide in a manner familiar to those versed in the art. A vitreous member also formed in the shape of a dome 32 serves to hermetically seal the upper portion of the cylindrical member I0. The above-describezi embodiment of the present invention is adapted to be directly inserted in a wave guide section of a wave guide system and when properly energized, as hereinbeiore described, will propagate such energy through said wave guide system.

Fig. 3 is a cross-sectional view taken along line 3-3 of Fig. 1 and clearly details the relative position of the cap 24 with respectl to the anode arms II. It also illustrates the manner in which said cap 24 is attached to the alternate anode arms II by means of the slots IIA. A :pair of electrically conductive straps 32-33 are connected, respectively, to the alternate and intervening anode arms to arrest the generation of spurious oscillations.

Fig. 4 is a perspective view 0f the invention wherein, for the sake of clarity, only a portion of the anode arms II are shown. together with a fragmentary view of the cap 24 and the tubular member 2B surmounting same. Here is clearly indicated the manner in which the cap 24 is disposed in the slots I IA provided in the alter nate anode arms Il. A second pair of electrically conductive straps 34-35, substantially identical with straps 32 and 33.` are connected, respectively to alternate and intervening anode arms.

Fig. 5 represents a third embodiment of the present invention. Whereas, the first and second embodiments were adapted to magnetrons, for example which employ twenty anode arms or less, it is necessary in the case of magnetrons employing more than twenty anode arms that the coupling cap 24, Figs. 1 and 2, be smaller in l its diametrical dimensions as the number of anode arms employed are increased beyond, for example, twenty arms. How the proper dimensions are arrived at will be discussed in connection with Figs. 6. 7, 8, 9, and 10.

In this third embodiment, the reduction of the diametrical proportions of the coupling cap makes its necessary to alter the type of pole piece used. It was found necessary to provide a pole piece 4U and a coupling cap 4I of the type illustrated. It will be appreciated that as the coupling cap dimensions were made smaller it was no longer possible to dispose the pole piece within said coupling cap because the gap between said pole piece and the external magnetizing means, not shown, would increase the reluctance path considerably. As a result of such increase in reluctance, the external magnetizing means would begin to assume proportions which would be bulky and uneconomical.

To overcome the aforesaid obstacles, the pole piece 40 was yprovided with a plurality of apertures 42 and the coupling cap 4I with an equal number of prongs 43 of suitable dimensions to enable them to pass freely, and without touching. through the apertures 42, the ends of said prongs being connected to the anode arms II within slots 44 provided therein. The pole piece 40 was made in the form of a thick shallow dish with an aperture 45 in the bottom thereof, said aperture being in register with the opening formed by the inner edges 46 of the anode arms Il. The aperture 45 permits one end of the cathode structure. see Fig. l to extend therethrough. The upper edge 4l of said pole piece is soldered within the cylindrical member ID, said member having a substantially thinner wall section 48 at this point of connection.

By yproviding a thin wall section at this point. the reluctance path, between the pole piece edge 41 and an external pole piece ring 49, is kept to a minimum, when suitable magnetizing means are attached to said pole piece ring 49.

For best results, the dimensions of the coupling cap should be such that the energy stored per cycle in the magnetron will have a certain ratio to the power dissipated in a matched load, This ratio will be designated hereinafter as the QE of an axial output electron discharge device of the type hereinbefore described.

Figs. 6 and 'I illustrate schematically the equivalent circuit of the above-described electron-discharge device in which Cr and Lr represent, respectively, the total capacity and inductance associated with said device, while Ear represents the total radio frequency voltage across the aforementioned CTLT combination. Rr is the total resistance or external load which will give th1 desired Qs when connected in parallel with said LT. Qa is determined by the following equation In the above equation o is 2r times the frequency of the fproper mode.

If, for example, a QE of the order of 200 is desired, in a magnetron employing twenty anode arms or less, RT becomes greater than 500 ohms, and it is therefore, not convenient to connect the load across ERF. However, it is practical to connect the load across a fraction of said Ear as illustrated in Fig. '7.

Now, in order to maintain the desired QE, the power delivered to the load must be the same as before, or

Film1@ RT R1 This may be Written M Li RT-R,

s 28,480 Therefore long line transmission theory. Lo is calculatedas follows: QF

mL: (rb-rl)[(`(rb+rl)t)] Knowing Qn it now remains to determine Ri and ZLI- N ,b rl Wh- Li as will be presently described. 1+3

Fig. 8 is a sketch of an axial output device of the type herein deseribedy the ieft hend View where 30,480 is a numerical constant that pro- With respect to the drawing beine a transverse vides a practical' unit (aah), N is the number oi cross-section looking along the axis Q of the lo anode armst 1S the thickness 0f Sald anode rjght hand View from right to le, said right armsalld the Other Symbols Ib, li and 1 are d1- nund View being a iongitudinei eross seetidn mensional values as indicated in Fig. 8. A value taken aione iine X X of the iefnhund vieu/ of ri can now be chosen and L1 and R1 deterwhile Fig. 9 represents an equivalent circuit of mmed, which Will Yield Q; 11 may n0W be adthe sketch in Fig. a. with reference to Fig. s, 16 Justed t0 Produce the desired Qa remembering rb, ri and l and li, said dimensions are in inches. that as 11 nc'eases- QE nCTeSeS- The impedance RL, Fig. qY ai; the terminals As a result of the simple and compact struc- C D wm be the characteristic impedance uf the ture herein described, the invention provides coaxial une at points C D in Fig. g The connovel means for transferring energy from each negtiog; for C D to A B is made by a plurality 20 resonant cavity, or any desired number of resoof prongs 43 which pass through apertures in the nant cavities, without the complicated structure pole piece shown in Fig. 5. The pole piece is not and plan-ning Suoh an arrangement would entaken into account in any of the caieuiations tail it one were to utilize such means as hairpin above or any to be described presently. Re transtype probes and the like. formed through the section of line between C-D The embOdimentS 0f the Present invention and B bemes the Ri needed to determine which have been illustrated and described have Qu, been selected for the purpose of setting forth The method used te determine the chamanthe principles involved. It will be obvious, howistie impedance' designated herein as zey of the ever, that the invention may be modified to meet Section C D te A B is as follows. various conditions which may be met with in dif- Assummg three prongs u were used to com ferent specific uses and it is, therefore, intended nece C D to AWBl the transmission une wm to cover by the appended claims all such modiappear as illustrated m Fig. lo when viewed treitgns viich fall within the spirit and scope of along its axis. Therefore s von on What is claimed is: Z 601 D,Il hm l. An electron dischargejdevice comprising: a Oglo s cathode; an anode structure spaced from said cathode and provided with a plurality of cavity Where Dm is the geometric moon distance be' resonators; a rst conductor connected to said tween a points on the outer oonduotol' 5o and 40 anode structure and constituting one of the conall points on the inner conductor 5I which. in ductors of a transmission line; a conductive cap the ease of one conductor completely enclosing connected to one or said cavity resonators in e the other, 1S the radius re 0f the Outer GOIldllCtOI. region of relatively low radio-frequency voltage; or Dm equals rn. De is the geometric mean dlsand a second conductor electrically connected to tance between all the points on the inner consaid cap said second conductor constituting the ductor, or the self-geometric mean distance. other conductor of said transmission line. The so-called self-geometricmean distance of a 2- An electrn discharge device COmDIiSiUSI 8 eireie is its radius The expression fori), is cathode; an anode structure spaced from said cathode and provided with less than a critical D.=DVa b c r number of cavity resonators; a first conductor e connected to said anode structure and constia=b=c D.=\/ar tuting one of the conductors of a transmission line; a conductive cap connected to one of said Where a" b and o are' respectively the distances cavity resonators in a region of relatively low between the centers of the prongs 3' n be g 6b radio-frequency voltage; and a second conductor equal to the number of prongs and r" the size of electrically connected to said cap said second the prongs, said size being as small as pOSSiblconductor constituting the other conductor of commensurate with the amount of power the Asind transmission iine, prongs are to carry. in order to minimize the Size 3. An electron discharge device comprising: an 0f the apertures in the D016 piece. 60 electrically conductive envelope; said envelope In the case of the i'lrst embodiment, wherein constituting the outer conductor of a transmisthe coupling cap 24 was entirely cylindrical, the sion line; a cathode mounted within said encalculations for determining D; would be based velope: a plurality of anode arms extending inon the number oi anode arms contacted by said Wardly from said envelope and Surrounding Said cap, each contact being considered a prong. o5 ChOde: each Pair Of adjoining anode arms, t0- Therefere' for n number df prongs eduuiiy gether with that portion of said envelope therespaced on the circumference oi a circle of rabetween' constituting a' cavity resonator; "n dius R electrically conductive cap, the open end oi which is connected to that portion of the alter- D n1 70 nate anode arms adacent said envelope; and ""\/(Rn1`/)n(nn(r n) an electrically conductive tubular member conn nected exteriorly to the closed end of said cap Using Rr. as a terminating impedance for e and constituting the inner conductor or said coaxial line of characteristic impedance Zo and transmission line. length li. the value oi Ri is found by ordinary 1I EXAMiNE 4. An electron-discharge device comprising:

an electrically conductive envelope; said envelope constituting the outer conductor of a transmission line; a cathode mounted within said envelope; a plurality of anode arms extending nwardly from said envelope and surrounding said cathode; each pair cf adjoining anode arms, together with that portion of said envelope therebetween, constituting a cavity resonator; an electrically conductive cap, the open end of which is connected to that portion of the alternate anode arms adjacent said envelope; an electrically conductive tubular member connected exteriorly to the closed end of said cap and constituting the inner conductor of said transmission line; and a pair of pole pieces, the eld of which extends longitudinally of said envelope, one of said pole pieces being disposed within said electrically conductive cap and the other oppositely disposed, with respect to said rst-narned pole piece, within said envelope.

[5. An electron discharge device adapted to be connected to a load having a predetermined resistive impedance comprising: an electrically conductive envelope; a conductor connected to said envelope and constituting the outer conductor of a transmission line; a cathode mounted within said envelope; a plurality of anode arms extending inwardly from said envelope and surrounding said cathode; each pair of adjoining anode arms, together with that portion of said envelope therebetween, constituting a cavity resonator; and an electrically conductive member. the open end of which is connected to a point on one of said anode arms, the distance between said point of connection Vand the axis of said envelope having a predetermined value satisfy- 'ing the equation LTR,

200:: CUL? where where in the equation lfor L1 N=the number of anode arms,

rb=the radius of the envelope with respect to its axis,

rl=the distance between the electrically conductive member and the axis of said envelope.

l=the length of the anode arms parallel with the axis of said envelope. and

t=the thickness of the anode arms, said electrically conductive member constituting the other conductor of said transmission line] 6. An electron discharge device comprising:

a cathode; an anode structure, spaced from said cathode, and incorporating a cavity resonator;

a transmission line including a pair of conductors electrically connected to spaced points on said cavity resonator; and a pair of pole pieces disposed adjacent said anode structure at opposite ends of said cavity resonator; one of said pole pieces being supported by one of the conductors of said transmission line.

7. An electron discharge device comprising: a. cathode; an anode structure, spaced from said cathode, and incorporating a cavity resonator; a transmission line including inner and outer conductors; said outer conductor being electrically connected to the exterior surface of said anode structure, and said inner conductor being provided with a coupling member electrically connected to a point on said cavity resonator; and a pair of pole pieces disposed adjacent said anode structure at opposite ends of said cavity resonator; one of said pole pieces being supported within the coupling member of the inner conductor of said transmission line.

8. An electron discharge device adapted to be connected to a load having a predetermined resistive impedance comprising: an electrically conductive envelope; a conductor connected to Said envelope and constituting the outer conductor of a transmission line; a cathode mounted within said envelope; a plurality of anode arms extending inwardly from said envelope and surrounding' said cathode; each pair of adjoining anode arms, together with that portion of said envelope therebetween, constituting a cavity resonator; and an electrically conductive member, the open end of which is connected to a point on one of said anode arms, the distance Ibetween said point of connection and the axis of said envelope having a predetermined value satisfying the equation where R1=the value of 'the resistive component of the impedance looking into the transmission line when said load is connected to said device,

Lr=totlal equivalent inductance of a cavity resonator,

w=21r times the frequency,

where in the equation for L1 REFERENCES CITED The following references are of record in the le of this patent or the original patent:

UNITED STATES PATENTS Number Name Date 2,414,085 Hartman Jan. 14, 1947 2,429,291 Okress Oct. 21, 1947 2,435,984 Spencer Feb. 17, 1948 2,442,118 Donal, Jr. et al. May 25, 1948 2,454,337 Okress Nov. 23, 1948 2,478,534 Kather Aug. 9, 1949 

